A snapshot is a copy of a set of files and/or directories as they were at a particular point in the past. That is, the snapshot is an image, or representation, of a volume of data at a point in time. A snapshot may be as a secondary copy of a primary volume of data, such as data in a file system, an Exchange server, a SQL database, an Oracle database, and so on. The snapshot may be an image of files, folders, directories, and other data objects within a volume, or an image of the blocks of the volume.
Data storage systems utilize snapshots for a variety of reasons. One typical use of snapshots is to copy a volume of data without disabling access to the volume for a long period. After performing the snapshot, the data storage system can then copy the data set by leveraging the snapshot of the data set. Thus, the data storage system performs a full backup of a primary volume when a primary volume is active and generating real-time data. Although performing a snapshot (i.e., taking an image of the data set) is a fast process, the snapshot is typically not an effective or reliable backup copy of a data set, because it does not actually contain the content of the data set. Restoring data from snapshots can be especially cumbersome, because a restoration process cannot restore the data set using snapshots alone. Recovery of individual files or folders can be especially cumbersome, because typical systems often recover an entire snapshot in order to restore an individual file or folder imaged by the snapshot.
Associated information, such as metadata, is often required in order to restore a file or folder via the snapshot, because the snapshot itself does not provide any information about the file or folder other than the image of a data set at a certain time. That is, the snapshot provides information about what was in or is changed in a data set (the image), but does not provide any information about where a particular file (or a copy of a data object) is currently stored or contained.
Therefore, a system that provides the benefits of snapshots while avoiding some of the drawbacks would provide significant utility.